Hi Dr. Bob, I first want to tank you for all your help. Secondly, I don't understand why this was marked wrong.
When 27.20mL of .5 M H2SO4 is added to 27.20 of 1M KOH in a coffee cup calorimeter at 23.5 degrees C, the temp rises to 30.17 degrees C. Calculate delta H of this reaction.
(Assume that the total volume is the sum of the individual volumes and that density and specific heat capacity of the solution are the same as pure water d of water =1.00g/mL: c of water =4.184J/g*c))
my work: correct or no??
• 2KOH + H2SO4→ 2H2O + K2SO4
n(KOH) = 0.0272 * 1 = 0.0272mol
n(H2SO4) =0.0272 * 0.5 = 0.0136 mol
total volume = 27.2 + 27.2 = 54.4mL
mass of solution = 54.4mL * 1g/mL =54.4g
Q = mcΔT
= 54.4g * 4.18 J/g°C * (30.17 - 23.5)°C
= 1516.74J
The heat is lost from system to surrounding, so ΔH is-ve
For every 0.0136 mol of H2SO4 react, it releases 1516.74J of heat
For 1 mole of H2SO4,
ΔH= 1516.74/0.0136
= -111.525 kJ / mol
= -112 kJ/ mol.......thank you, sir•chemistry/check my work I have to submit today - DrBob222, Saturday, October 17, 2015 at 1:06am
The heat is lost from system to surrounding, so ΔH is-ve
For every 0.0136 mol of H2SO4 react, it releases 1516.74J of heat
For 1 mole of H2SO4,
ΔH= 1516.74/0.0136
= -111.525 kJ / mol
= -112 kJ/ mol.......thank you, sIr
This value is for 2 mols H2O so you need to to do -112 kJ/mol x 1/2 = about 56 kJ/mol.
•Is that a -56 ?•chemistry-Dr Bob - DrBob222, Sunday, October 18, 2015 at 11:43am
Yes, of course. I dropped the - sign on the last step.
it said hint:
What is the balanced equation for this acid base neutralization reaction? First find q by multiplying the total mass of the solution by the change in temperature and the specific heat capacity of water. Once you have found q , divide q ( in kj) by the moles of H2SO4 to find the heat of reaction in units of kj/mol . In the question , the volume of the solution are given in units of ml. How would you find the solution masses in grams from the density of water? How would you find the moles of H2SO4 from the volume and concentration of H2SO4?
thank you again, Dr. Bob
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